A typical vane-type camshaft phaser for changing the phase relationship between a crankshaft and a camshaft of an internal combustion engine generally comprises a plurality of outwardly-extending vanes on a rotor interspersed with a plurality of inwardly-extending lobes on a stator, forming alternating advance and retard chambers between the vanes and lobes. A back cover and a front cover are used to close off respective sides of the advance chambers and the retard chambers such that fasteners are used to clamp the stator between the front cover and the back cover. Engine oil is selectively supplied to either the advance or retard chambers and vacated from the other of the advance and retard chambers by an oil control valve in order to rotate the rotor within the stator and thereby change the phase relationship between an engine camshaft and an engine crankshaft.
German patent application publication number DE 102010010205 A1 to Gautier, hereinafter referred to as Gautier, shows an example of a camshaft phaser as previously described. Gautier teaches that a toothed pulley is spaced radially outward from the stator such that the toothed pulley is integrally formed with the back cover. The stator is clamped between the back cover and the front cover by a plurality of cover bolts which extend through apertures formed in each of the lobes of the stator in order to seal the advance and retard chambers between the back cover and the front cover. However, the stator of Gautier includes five lobes spaced substantially equally around the stator. Consequently, five equally spaced cover bolts provide a clamping force to clamp the stator between the back cover and the front cover. While five equally spaced cover bolts may be sufficient to clamp the stator between the back cover and the front cover, some camshaft phasers have stators with fewer lobes or with lobes that are not equally spaced. Consequently, cover bolts that pass through apertures in the lobes may not provide an adequate clamping force to provide a proper seal between the back cover and the stator and between the front cover in all stator designs. Furthermore, some camshaft phasers have stators with lobes that are not sufficiently large to accommodate cover bolts passing therethrough.
EP patent application publication EP 2058478 A1 to Sluka et al., hereinafter referred to as Sluka et al., shows another example of a camshaft phaser as previously described. Sluka et al. teaches a stator having an inner stator wall from which three lobes extend radially inward. The stator also includes an outer stator wall formed integrally therewith which is spaced radially outward from the outer stator wall such that the outer stator wall includes pulley teeth on the outer circumference thereof. The stator also includes a front cover formed integrally therewith which closes off one side of the advance chambers and the retard chambers. A back cover is clamped to the stator using cover bolts in order to close off the other side of the advance chambers and the retard chambers. A plurality of ribs extend radially between the inner stator wall and the out stator wall such that three of the ribs are sufficiently large to accommodate apertures for receiving cover bolts which clamp the front cover to the stator. The ribs extend axially the same distance as the inner stator wall; consequently, the ribs carry a clamping force from the cover bolts. While the stator of Sluka et al. allows the placement of the cover bolts to be independent of the location of the lobes of the stator, the ribs which receive cover bolts can be difficult to form in stators that are made using powder metal process. Furthermore, the ribs add weight to the stator which goes against the desire to minimize weight in order to maximize fuel efficiency of motor vehicles.
What is needed is camshaft phaser which minimizes or eliminates one or more the shortcomings as set forth above.